Comparative Study on the Thermal and Electrical Properties of Copper-Filled PMMA and Unsaturated Polyester Composites Fabricated via Casting

Poly(methyl methacrylate) (PMMA)/Copper (PMMA/Cu) and unsaturated polyester/copper (UP/Cu) microcomposites were fabricated via solvent and liquid casting with 0 to 45 wt.% copper particles. X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed phase purity, showing that UP matrix curing shrinkage (7%-10%) induced tighter particle proximity than PMMA. Lee’s disk measurements showed rising thermal conductivity k. Pristine UP (0.14 W/mK) and neat PMMA (0.08 W/mK) reached 1.11 and 1.05 W/mK at wt.% Cu. UP/Cu achieved a 75% performance leap (0.51 vs. 0.29 W/mK) at 15 wt.% loading by reducing Kapitza resistance. From 5 kHz to 1 MHz, the dielectric constant climbed from 2.0 to 10.0 for PMMA/Cu and from 12.2 to 23.3 for UP/Cu at 45 wt.%, driven by Maxwell–Wagner–Sillars interfacial polarization and microcapacitor networks. Alternating current conductivity followed Jonscher’s power law via localized charge hopping. Thermally activated direct current measurements (30 to 80 °C) showed activation energy Ea collapsed from 0.41 to 0.31 eV for PMMA/Cu and from 0.40 to 0.29 eV for UP/Cu. High-frequency transport dominated direct current by seven orders of magnitude as microcapacitive currents bypassed potential barriers.